This invention relates to a data link for digital systems over moderate distances, and more particularly to a system for full duplex communications between digital systems in a noisy environment.
As part of an antenna automation project being conducted for space exploration, a need arose for a high-speed, full duplex communication link between a microprocessor located in the structure of the antenna and a minicomputer located approximately 500 meters away in a control room. The harsh electrical environment necessitated a data link that is resistant to ground loops and large noise spikes. This generally requires a very large and complex data link. What led to the present invention was a desire for a simpler, and therefore less expensive data link.
An object was desired to make the link hardware as insensitive to environmentally induced faults as possible while keeping it reasonably simple. The philosophy taken was to accept faults occurring with low to moderate probability but with high probability that the system can recover from a fault given that a fault has occurred. So fault detection is as important in the link design as fault prevention. Clearly, since the most probable type of fault, i.e., single bits, burts, etc., is a function of the nature of the electrical environment, a provision was made for allowing various fault detection schemes or combinations of schemes in different applications according to the needs of the particular applications. That could best be handled by either software or hardware in host-specific interface units, although some fault detection schemes could well be implemented as part of the link hardware, such as parity encoding and checking.